1. Field of Invention
The present invention relates to a valve device. More specifically, it relates to configuration of a valve seat plate which is used in the valve device.
2. Description of Related Art
In refrigerators, a valve device is used to distribute a common refrigerant (fluid) to a plurality of compartments to cool them. As illustrated in FIGS. 6(A) and (B), such a valve device comprises a valve seat plate 13′ having a refrigerant inlet opening 13c and refrigerant outlet openings 13a and 13b through which a refrigerant flows in the thickness direction, a sealing case (not illustrated) which covers a front surface of the valve seat plate 13′, and a valve element (not illustrated) which rotates on the front surface of the valve seat plate 13′ to open and close the refrigerant outlets 13a and 13b. Also, a rotor support shaft 18 and a valve element support shaft 35 are fixed to the valve seat plate 13′.
In the valve seat plate 13′, the inlet opening 13c and outlet openings 13a and 13b are formed as holes, each of which has a small diameter portion on the front side and a large diameter portion on the back side. The portions of different diameters are connected by a step. The large diameter portions of the inlet opening 13c and outlet openings 13a and 13b on the back surface side are the holes for inserting pipes. Inlet pipe 28c and outlet pipes 28a and 28b are brazed to the respective pipe-inserting holes with the incoming ends thereof in contact with the steps.
In a valve device having such a configuration, the area of the outlet openings 13a and 13b in the front surface of the valve seat plate 13′ is the surface on which the valve element rotates. Therefore, this area of the front surface of the valve seat plate 13′ is required to have high surface precision so that the flow of the refrigerant is completely cut off. Also, the valve seat plate 13′ needs to have a thickness such that the surface on which the valve element rotates does not warp even when heated to the temperature of 1000° C. or above for fixing the pipes 28a, 28b and 28c by brazing. Further, the valve seat plate 13′ needs to be composed of a ferrous material so that it can be brazed, and SUS is used because of its excellent corrosion resistance.
For these reasons, when the valve seat plate 13′ is manufactured conventionally, a thick SUS needs to be lathed, which increases the cost of the valve seat plate 13′.
Although forging may be considered in place of lathing, as a manufacturing method for a valve seat plate, it is also an expensive method though not as costly as lathing. In addition, when it is a sintered body, a hole-sealing process is required. Also, it is difficult to obtain precise dimensions and positions of the holes. Also, forging creates a great residual stress on the surface; therefore, when brazed, the surface which requires high precision is warped due to the heat of the brazing.
A sinter molding may also be considered in place of lathing as a manufacturing method for a valve seat plate. However, this method is also expensive though not as costly as lathing. In addition, when a sintered body is used, a hole-sealing process is required. However, resin-impregnation, a common hole-sealing process, is problematic because the resin cannot resist the brazing temperature. Further, since a sintered body is low in surface hardness, its resistance against the rotation of the valve element is also poor. Furthermore, sintering restricts the smallest formable hole diameter. For example, to form a hole with a diameter of 1.5φ by sintering, a lathing process is required as a secondary process.
Considering the above problems, an object of the present invention is to provide a valve device in which pipes can be installed without causing warping on the area of the surface on which a valve element rotates, and which can reduce the manufacturing cost of a valve seat plate.